Effect of phase shift on transmission characteristics of cascaded long-period fiber gratings is analyzed using transfer matrix methods based on coupled-mode theory.When the phase shift changed from 0 to π,a little stop band appeared on the left of the main stop band.The greater the amount of phase shift,the bigger the amplitude of the small stop band.When phase shift increases to π,amplitude of small stop band is equal to that of the original stop band.When the phase shift changes from π to 2π,a little stop band appeared on the right of the main stop band.The greater the amount of phase shift,the smaller the amplitude of the small stop band.With the increase of the phase shift,the peak of the resonance wavelength of the main stop band shifts to the long wavelength direction.The resonant wavelength can be flexibly changed by adjusting phase shift.The research provides theoretical foundation for the development of new fiber grating devices.